Light-emitting compound

ABSTRACT

A compound of formula (I): wherein M is a transition metal; Ar 1  is a 5 or 6 membered heteroaryl ring or a polycyclic heteroaromatic group; Ar 2  is a polycyclic group comprising two or more rings selected from aromatic and heteroaromatic rings; Ar 1  and Ar 2  may be linked by a direct bond or divalent linking group; L is a ligand; x is at least 1; a, b and y are each 0 or a positive integer; R 1 , R 2  and R 3  are each independently a substituent; and (i) Ar 1  is a polycyclic heteroaromatic group; or (ii) Ar 1  is a 5 or 6 membered heteroaryl ring and Ar 2  is a polycyclic group comprising at least 3 rings selected from aromatic and heteroaromatic rings. The compound may be used as an infra-red emitting material of an organic light-emitting device.

FIELD OF THE INVENTION

The present invention relates to phosphorescent light-emittingcompounds; compositions, solutions and light-emitting devices comprisingsaid light-emitting compounds; and methods of making said light-emittingdevices.

BACKGROUND OF THE INVENTION

Electronic devices containing active organic materials are attractingincreasing attention for use in devices such as organic light emittingdiodes (OLEDs), organic photoresponsive devices (in particular organicphotovoltaic devices and organic photosensors), organic transistors andmemory array devices. Devices containing active organic materials offerbenefits such as low weight, low power consumption and flexibility.Moreover, use of soluble organic materials allows use of solutionprocessing in device manufacture, for example inkjet printing orspin-coating.

An OLED may comprise a substrate carrying an anode, a cathode and one ormore organic light-emitting layers between the anode and cathode.

Holes are injected into the device through the anode and electrons areinjected through the cathode during operation of the device. Holes inthe highest occupied molecular orbital (HOMO) and electrons in thelowest unoccupied molecular orbital (LUMO) of a light-emitting materialcombine to form an exciton that releases its energy as light.

A light emitting layer may comprise a semiconducting host material and alight-emitting dopant wherein energy is transferred from the hostmaterial to the light-emitting dopant. For example, J. Appl. Phys. 65,3610, 1989 discloses a host material doped with a fluorescentlight-emitting dopant (that is, a light-emitting material in which lightis emitted via decay of a singlet exciton).

Phosphorescent dopants are also known (that is, light-emitting dopantsin which light is emitted via decay of a triplet exciton).

Suitable light-emitting materials include small molecule, polymeric anddendrimeric materials. Suitable light-emitting polymers includepoly(arylene vinylenes) such as poly(p-phenylene vinylenes) andpolyarylenes such as polyfluorenes.

OLEDs containing red, green and blue light-emitting materials forapplications such as displays and lighting are known.

OLEDs containing infrared emitting materials are also known as disclosedin, for example, Chuk-Lam Ho, Hua Li and Wai-Yeung Wong, “Red tonear-infrared organometallic phosphorescent dyes for OLED applications”,J. Organomet. Chem. 751 (2014), 261-285. However, a problem associatedwith infrared emitting OLEDs is low efficiency.

It is an object of the invention to improve the efficiency of infraredemitting OLEDs.

SUMMARY OF THE INVENTION

In a first aspect the invention provides a compound of formula (I):

wherein:

M is a transition metal;

Ar¹ is a 5 or 6 membered heteroaryl ring or a polycyclic heteroaromaticgroup;

Ar² is a polycyclic group comprising two or more rings selected fromaromatic and heteroaromatic rings;

Ar¹ and Ar² may be linked by a direct bond or divalent linking group;

L is a ligand;

x is at least 1;

y is 0 or a positive integer;

a is 0 or a positive integer;

b is 0 or a positive integer;

R¹, R² and R³ are each independently a substituent; and

-   -   (i) Ar¹ is a polycyclic heteroaromatic group; or    -   (ii) Ar¹ is a 5 or 6 membered heteroaryl ring and Ar² is a        polycyclic group comprising at least 3 rings selected from        aromatic and heteroaromatic rings.

In a second aspect the invention provides a composition comprising ahost material and a compound according to the first aspect.

In a third aspect the invention provides a solution comprising acompound or composition according to the first or second aspectdissolved in one or more solvents.

In a fourth aspect the invention provides an organic light-emittingdevice comprising an anode, a cathode and a light-emitting layer betweenthe anode and cathode wherein the light-emitting layer comprises acompound or composition according to the first or second aspect.

In a fifth aspect the invention provides a method of forming an organiclight-emitting device according to claim the fourth aspect, the methodcomprising the step of depositing the light-emitting layer over one ofthe anode and cathode, and depositing the other of the anode and cathodeover the light-emitting layer.

DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to theFIGURES, in which:

FIG. 1 illustrates an OLED according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1, which is not drawn to any scale, illustrates schematically anOLED 100 according to an embodiment of the invention. The OLED 100 iscarried on substrate 107 and comprises an anode 101, a cathode 105 and alight-emitting layer 103 between the anode and the cathode. Furtherlayers (not shown) may be provided between the anode and the cathodeincluding, without limitation, hole-transporting layers,electron-transporting layers, hole-blocking layers, electron-blockinglayers, hole-injection layers and electron-injection layers.

Exemplary OLED structures including one or more further layers includethe following:

Anode/Hole-injection layer/Light-emitting layer/Cathode

Anode/Hole transporting layer/Light-emitting layer/Cathode

Anode/Hole-injection layer/Hole-transporting layer/Light-emittinglayer/Cathode

Anode/Hole-injection layer/Hole-transporting layer/Light-emittinglayer/Electron-transporting layer/Cathode.

Light-emitting layer 103 may contain a host material and aphosphorescent compound of formula (I).

The device may contain more than one light-emitting layer. Thelight-emitting layer or layers may contain the phosphorescent compoundof formula (I) and one or more further light-emitting compounds, forexample further phosphorescent or fluorescent light-emitting materialshaving a colour of emission differing from that of the compound offormula (I). Preferably, light-emitting layer 103 is the onlylight-emitting layer of the device. Preferably, at least 90% or 95% ofthe light emitted by the device when in use, more preferably all light,is light emitted from the compound of formula (I).

Compounds of formula (I) preferably have a photoluminescence spectrumwith a peak of at least 650 nm, optionally in the range of 650-1000 nm,preferably 700-850 nm.

The photoluminescence spectrum of a compound of formula (I) may bemeasured by casting 5 wt % of the material in a polystyrene film onto aquartz substrate and measuring in a nitrogen environment using apparatusC9920-02 supplied by Hamamatsu.

Metal M of the phosphorescent compound of formula (I) may be anysuitable transition metal, for example a transition metal of the secondor third row of the d-block elements (Period 5 and Period 6,respectively, of the Periodic Table). Exemplary metals includeRuthenium, Rhodium, Palladium, Silver, Tungsten, Rhenium, Osmium,Iridium, Platinum and Gold. Preferably, M is iridium.

The compound of formula (I) may contain one or more ligands L other thanligands of formula:

Ligand L, if present, may be a monodentate or polydentate ligand.Optionally, L is a bidentate ligand. Optionally, L is selected from O,Ocyclometallating ligands; N,O cyclometallating ligands, optionallypicolinate; and N,N cyclometallating ligands.

L may be a ligand of formula:

wherein R¹⁶ in each occurrence is independently a substituent,preferably C₁₋₁₀ alkyl and R¹⁷ is H or a substituent, preferably H orC₁₋₁₀ alkyl; and wherein one R¹⁶ and R¹⁷ may be linked to form a ring,optionally a 6-10 membered aromatic or heteroaromatic ring that may beunsubstituted or substituted with one or more substituents, optionallyone or more substituents selected from C₁₋₂₀ hydrocarbyl groups.

Preferably R¹⁶ is C₁₋₄ alkyl, more preferably methyl or tert-butyl.

Preferably, y is 0 or 1.

The compound of formula (I) comprises at least one ligand of formula:

In case (i) Ar¹ is a polycyclic heteroaromatic group and Ar² is apolycyclic group comprising at least 2 rings selected from aromatic andheteroaromatic rings.

By “polycyclic heteroaromatic group” as used herein is meant apolycyclic group comprising a heteroaromatic ring and further comprisingone or more rings selected from aromatic and heteroaromatic rings. Therings of the polycyclic heteroaromatic group may consist of fusedheteroaromatic or aromatic rings or may comprise one or morenon-aromatic rings. Preferably, all aromatic or heteroaromatic rings ofthe polycyclic heteroaromatic group are conjugated to each otherdirectly or through one or more intervening aromatic or heteroaromaticrings.

In case (ii) Ar¹ is a monocyclic 5 or 6 membered heteroaryl ring and Ar²is a polycyclic group comprising at least 3 rings selected from aromaticand heteroaromatic rings.

The polycyclic group Ar² may consist of fused heteroaromatic or aromaticrings or may comprise one or more non-aromatic rings. Preferably, allaromatic or heteroaromatic rings of the polycyclic group Ar² areconjugated to each other directly or through one or more interveningaromatic or heteroaromatic rings.

A polycyclic group Ar¹ or Ar² may be a 10-30 membered polycyclic group.

In case (i), Ar¹ is optionally a 10-membered polycyclic heteroaromaticof C and N atoms, optionally a polycyclic heteroaromatic of pyridine orpyrazine fused to any of benzene, pyridine or pyrazine. Ar¹ ispreferably selected from quinoline or isoquinoline. Optionally, theligand Ar¹-Ar² is selected from the following ligands wherein thequinoline or isoquinoline group is substituted with a triazine group asillustrated in Formula (I) and optionally with one or more substituentsR¹ and wherein Ar² is unsubstituted or substituted with one or moresubstituents R²:

In case (i), optionally Ar² is selected such that ligand Ar¹-Ar² isselected from the following ligands wherein Ar¹ may be substituted withone or more substituents R¹ and wherein Ar² is unsubstituted orsubstituted with one or more substituents R²:

wherein X in each occurrence is independently CR² ₂, SiR² ₂, NR², O or Swherein R² independently in each occurrence is a substituent.

In case (ii), Ar¹ is a monocyclic 5 or 6 membered heteroaromatic ring,preferably a 6-membered heteroaromatic ring of C and N atoms, preferablypyridine, and Ar² is preferably a polyaromatic group, optionally aC₁₀₋₂₀ polyaromatic compound. Preferably, Ar² of case (ii) is apolyaromatic hydrocarbon of 3 or more fused benzene rings, preferablyphenanthrene, that may be unsubstituted or substituted with one or moresubstituents R².

In either case (i) or (ii) there may be a direct bond or divalentlinking group between Ar¹ and Ar² (in addition to the C—C bond shown inFormula (I) between Ar¹ and Ar²).

R¹ and R², if present, may independently in each occurrence be selectedfrom the group consisting of:

-   -   C₁₋₂₀ alkyl wherein one or more non-adjacent C atoms of the        C₁₋₂₀ alkyl may be replaced with —O—, —S—, C═O or —COO— and one        or more H atoms may be replaced with F; and    -   a group of formula —(Ar³)p wherein Ar³ in each occurrence is a        C₆₋₂₀ aryl group or a 5-20 membered heteroaryl group that may be        unsubstituted or substituted with one or more substituents; and        p is at least 1, optionally 1, 2 or 3.

Substituents of Ar³, if present, are optionally selected from the groupconsisting of F, CN, NO₂ and C₁₋₂₀ alkyl wherein one or morenon-adjacent C atoms of the C₁₋₂₀ alkyl may be replaced with —O—, —S—,C═O or —COO— and one or more H atoms may be replaced with F. If present,the one or more substituents of Ar³ are preferably selected from C₁₋₂₀alkyl.

Optionally, R³ in each occurrence is independently selected from thegroup consisting of:

-   -   C₁₋₂₀ alkyl wherein one or more non-adjacent C atoms of the        C₁₋₂₀ alkyl may be replaced with —O—, —S—, C═O or —COO— and one        or more H atoms may be replaced with F; and    -   a group of formula —(Ar⁴)q wherein Ar⁴ in each occurrence is a        C₆₋₂₀ aryl group or a 5-20 membered heteroaryl group that may be        unsubstituted or substituted with one or more substituents; and        q is at least 1.

Substituents of Ar⁴, if present, are optionally selected from the groupconsisting of F, CN, NO₂ and C₁₋₂₀ alkyl wherein one or morenon-adjacent C atoms of the C₁₋₂₀ alkyl may be replaced with —O—, —S—,C═O or —COO— and one or more H atoms may be replaced with F. If present,the one or more substituents of Ar4 are preferably selected from C₁₋₂₀alkyl.

Preferably, R³ is phenyl that may be unsubstituted or substituted withone or more substituents.

The triazine substituent of formula (I) may be bound to any availableposition of Ar¹, preferably an aromatic carbon atom of Ar¹. Preferably,the triazine substituent is bound to an atom meta-to the N atom of Ar¹that is bound to M.

Exemplary compounds of formula (I) according to case (i) include thefollowing:

Exemplary compounds of formula (I) according to case (ii) include thefollowing:

Host Material

The host material has a triplet excited state energy level T₁ that is nomore than 0.1 eV lower than, and preferably at least the same as orhigher than, the phosphorescent compound of formula (I) in order toallow transfer of triplet excitons from the host material to thephosphorescent compound of formula (I).

The triplet excited state energy levels of a host material and aphosphorescent compound may be determined from the energy onset of itsphosphorescence spectrum measured by low temperature phosphorescencespectroscopy (Y. V. Romaovskii et al, Physical Review Letters, 2000, 85(5), p 1027, A. van Dijken et al, Journal of the American ChemicalSociety, 2004, 126, p 7718).

The host material preferably has a lowest unoccupied molecular orbital(LUMO) level of at least 2.5 eV from vacuum.

The host material may be a polymer or a non-polymeric material.

The compound of formula (I) may be blended with or covalently bound tothe host material.

The metal complex of formula (I) may be provided in an amount in therange of 0.1-40 wt % in a composition comprising a mixture of the hostand the metal complex of formula (I).

In the case of a host polymer the compound of formula (I) may beprovided as a side-group or end group of the polymer backbone or as arepeat unit in the backbone of the polymer. In this case, repeat unitscomprising a compound of formula (I) may form 0.1-40 mol % of the repeatunits of the polymer.

A host polymer may comprise a repeat unit of formula (V):

wherein Ar⁵ and Ar⁶ are each independently aryl or heteroaryl that maybe unsubstituted or substituted with one or more, optionally 1, 2, 3 or4, substituents; u and v in each occurrence is independently at least 1,optionally 1, 2 or 3, preferably 1; R⁶ is a substituent; and Y is N orCR⁹, wherein R⁹ is H or a substituent, preferably H or C₁₋₁₀ alkyl andwith the proviso that at least one Y is N.

Preferably, Ar⁵ and Ar⁶ and are each independently unsubstituted orsubstituted C₆₋₂₀ aryl, more preferably C₁₀₋₂₀ aryl. Exemplary groupsAr⁵ and Ar⁶ are phenyl and naphthyl, preferably naphthyl.

Preferably, R⁶ is a C₁₋₂₀ alkyl group or a group of formula —(Ar⁷)wwherein Ar⁷ independently in each occurrence is an aryl or heteroarylgroup that may be unsubstituted or substituted with one or more,optionally 1, 2, 3 or 4, substituents and w is at least 1, optionally 1,2 or 3. Preferably, each Ar⁷ is independently selected fromunsubstituted or substituted phenyl, pyridyl, pyrimidine, pyrazine andtriazine.

Substituents of Ar⁵, Ar⁶ and Ar⁷ may be selected from substituted orunsubstituted alkyl, optionally C₁₋₂₀ alkyl, wherein one or morenon-adjacent C atoms may be replaced with O, S, C═O or —COO— and one ormore H atoms may be replaced with F.

In one preferred embodiment, all 3 groups Y are N.

Preferably, u and v are each 1.

Preferably, w is 1, 2 or 3.

Exemplary repeat units of formula (V) have the following structureswhich may be unsubstituted or substituted with one or more substituents,preferably one or more C₁₋₂₀ alkyl groups:

A host polymer may comprise a repeat unit of formula (XI):

wherein each R¹¹ is independently H or a substituent. Optionally,substituents R¹¹ are independently selected from C₆₋₂₀ aryl that may beunsubstituted or substituted with one or more substituents, optionallyone or more C₁₋₁₀ alkyl groups, and C₁₋₂₀ alkyl wherein one or morenon-adjacent C atoms may be replaced with O, S, COO or CO and one ormore H atoms may be replaced with F. Preferably, each R¹¹ isindependently selected from H and C₁₋₂₀ alkyl.

A host polymer may comprise a repeat unit of formula (VI):

wherein Ar⁸, Ar⁹ and Ar¹⁰ in each occurrence are independently selectedfrom substituted or unsubstituted aryl or heteroaryl, g is 0, 1 or 2,preferably 0 or 1, R¹³ independently in each occurrence is asubstituent, and d, e and f are each independently 1, 2 or 3.

R¹³, which may be the same or different in each occurrence when g is 1or 2, is preferably selected from the group consisting of alkyl,optionally C₁₋₂₀ alkyl, Ar¹¹ and a branched or linear chain of Ar¹¹groups wherein Ar¹¹ in each occurrence is independently substituted orunsubstituted aryl or heteroaryl.

Any two aromatic or heteroaromatic groups selected from Ar⁸, Ar⁹, and,if present, Ar¹⁰ and Ar¹¹ that are directly bound to the same N atom maybe linked by a direct bond or a divalent linking atom or group.Preferred divalent linking atoms and groups include 0, S; substituted N;and substituted C.

Ar⁸ and Ar¹⁰ are preferably C₆₋₂₀ aryl, more preferably phenyl, that maybe unsubstituted or substituted with one or more substituents.

In the case where g=0, Ar⁹ is preferably C₆₋₂₀ aryl, more preferablyphenyl, that may be unsubstituted or substituted with one or moresubstituents.

In the case where g=1, Ar⁹ is preferably C₆₋₂₀ aryl, more preferablyphenyl or a polycyclic aromatic group, for example naphthalene,perylene, anthracene or fluorene, that may be unsubstituted orsubstituted with one or more substituents.

R¹³ is preferably Ar¹¹ or a branched or linear chain of Ar¹¹ groups.Ar¹¹ in each occurrence is preferably phenyl that may be unsubstitutedor substituted with one or more substituents.

Exemplary groups R¹³ include the following, each of which may beunsubstituted or substituted with one or more substituents, andwherein * represents a point of attachment to N:

d e and f are preferably each 1.

Ar⁸, Ar⁹, and, if present, Ar¹⁰ and Ar¹¹ are each independentlyunsubstituted or substituted with one or more, optionally 1, 2, 3 or 4,substituents. Exemplary substituents may be selected from substituted orunsubstituted alkyl, optionally C₁₋₂₀ alkyl, wherein one or morenon-adjacent C atoms may be replaced with optionally substituted aryl orheteroaryl (preferably phenyl), O, S, C═O or —COO— and one or more Hatoms may be replaced with F.

Preferred substituents of Ar⁸, Ar⁹, and, if present, Ar¹⁰ and Ar¹¹ areC₁₋₄₀ hydrocarbyl, preferably C₁₋₂₀ alkyl.

Preferred repeat units of formula (VI) include unsubstituted orsubstituted units of formulae (VI-1), (VI-2) and (VI-3):

A host polymer may comprise arylene repeat units, preferably C₆₋₂₀arylene repeat units, which may be unsubstituted or substituted with oneor more substituents. Exemplary arylene repeat units are phenylene,fluorene, indenofluorene and phenanthrene repeat units, each of whichmay be unsubstituted or substituted with one or more substituents.Preferred substituents are selected from C₁₋₄₀ hydrocarbyl groups.

Arylene repeat units may be selected from formulae (VII)-(X):

wherein tin each occurrence is independently 0, 1, 2, 3 or 4, preferably1 or 2; R⁷ independently in each occurrence is a substituent; s in eachoccurrence is independently 0, 1 or 2, preferably 0 or 1; and R⁸independently in each occurrence is a substituent wherein two R⁸ groupsmay be linked to form an unsubstituted or substituted ring.

Where present, each R⁷ and R⁸ may independently be selected from thegroup consisting of:

-   -   alkyl, optionally C₁₋₂₀ alkyl, wherein one or more non-adjacent        C atoms may be replaced with optionally substituted aryl or        heteroaryl, O, S, substituted N, C═O or —COO—, and one or more H        atoms may be replaced with F;    -   aryl and heteroaryl groups, preferably C₆₋₂₀ aryl groups, more        preferably phenyl, that may be unsubstituted or substituted with        one or more substituents; and    -   a linear or branched chain of aryl or heteroaryl groups,        preferably C₆₋₂₀ aryl groups, more preferably phenyl, each of        which groups may independently be substituted, optionally a        group of formula —(Ar¹²)_(r) wherein each Ar¹² is independently        an aryl or heteroaryl group and r is at least 2, preferably a        branched or linear chain of phenyl groups.

In the case where R⁷ or R⁸ comprises an aryl or heteroaryl group, or alinear or branched chain of aryl or heteroaryl groups, the or each arylor heteroaryl group may be substituted with one or more substituents R⁸selected from the group consisting of:

-   -   alkyl, for example C₁₋₂₀ alkyl, wherein one or more non-adjacent        C atoms may be replaced with O, S, substituted N, C═O and —COO—        and one or more H atoms of the alkyl group may be replaced with        F;

NR⁹ ₂, OR⁹, SR⁹, SiR⁹ ₃ and

-   -   fluorine, nitro and cyano;

wherein each R⁹ is independently selected from the group consisting ofalkyl, preferably C₁₋₂₀ alkyl; and aryl or heteroaryl, preferablyphenyl, optionally substituted with one or more C₁₋₂₀ alkyl groups.

Substituted N, where present, may be —NR¹⁰— wherein R¹⁰ is a substituentand is optionally a C₁₋₄₀ hydrocarbyl group, optionally a C₁₋₂₀ alkylgroup.

Preferred substituents of aryl or heteroaryl groups of R⁷ or R⁸ areselected from C₁₋₂₀ alkyl.

In the case where two groups R⁸ form a ring, the one or moresubstituents of the ring, if present, are optionally selected from C₁₋₂₀alkyl groups.

Preferably, each R⁷, where present, and R⁸ is independently selectedfrom C₁₋₄₀ hydrocarbyl. Preferred C₁₋₄₀ hydrocarbyl groups are C₁₋₂₀alkyl; unsubstituted phenyl; phenyl substituted with one or more C₁₋₂₀alkyl groups; and a linear or branched chain of phenyl groups, whereineach phenyl may be unsubstituted or substituted with one or more C₁₋₂₀alkyl groups.

A host polymer may comprise or consist of repeat units of formula (V),(VI) and/or (XI) and one or more arylene repeat units as describedherein, optionally one or more arylene repeat units of formulae(VII)-(X).

Repeat units of formulae (V), (VI) and/or (XI) may each be provided inthe host polymer in an amount in the range of 1-50 mol %, optionally5-50 mol %.

Arylene repeat units may form 1-99 mol %, preferably 10-95 mol % of therepeat units of a host polymer.

Polymers as described herein including, without limitation, hostpolymers, may have a polystyrene-equivalent number-average molecularweight (Mn) measured by gel permeation chromatography in the range ofabout 1×10³ to 1×10⁸, and preferably 1×10³ to 5×10⁶. Thepolystyrene-equivalent weight-average molecular weight (Mw) of thepolymers described herein may be 1×10³ to 1×10⁸, and preferably 1×10⁴ to1×10⁷.

Polymers as described herein including, without limitation, hostpolymers, are preferably amorphous.

Charge Transporting and Charge Blocking Layers

A hole transporting layer may be provided between the anode of an OLEDand a light-emitting layer containing a compound of formula (I).

An electron transporting layer may be provided between the cathode of anOLED and a light-emitting layer containing a compound of formula (I).

An electron blocking layer may be provided between the anode and thelight-emitting layer.

A hole blocking layer may be provided between the cathode and thelight-emitting layer.

Transporting and blocking layers may be used in combination. Dependingon its HOMO and LUMO levels, a single layer may both transport one ofholes and electrons and block the other of holes and electrons.

A charge-transporting layer or charge-blocking layer may be crosslinked,particularly if a layer overlying that charge-transporting orcharge-blocking layer is deposited from a solution. The crosslinkablegroup used for this crosslinking may be a crosslinkable group comprisinga reactive double bond such and a vinyl or acrylate group, or abenzocyclobutane group. The crosslinkable group may be provided as asubstituent pendant from the backbone of a charge-transporting orcharge-blocking polymer. Following formation of a charge-transporting orcharge blocking layer, the crosslinkable group may be crosslinked bythermal treatment or irradiation.

If present, a hole transporting layer located between the anode and thelight-emitting layer containing the compound of formula (I) preferablycontains a hole-transporting material having a HOMO level of less thanor equal to 5.5 eV, more preferably around 4.8-5.5 eV as measured bycyclic voltammetry. The HOMO level of the hole transporting material ofthe hole-transporting layer may be selected so as to be within 0.2 eV,optionally within 0.1 eV, of the compound of formula (I) in order toprovide a small barrier to hole transport.

A hole-transporting material of a hole-transporting polymer may be apolymer comprising a repeat unit of formula (VI) as described herein,optionally a homopolymer of a repeat unit of formula (VI) or a copolymercomprising a repeat unit of formula (VI) and one or more co-repeatunits, optionally one or more arylene co-repeat units as describedherein. One or more repeat units of such a hole-transporting polymer maybe substituted with a crosslinkable group, optionally a crosslinkabledouble bond group and/or a crosslinkable benzocyclobutane group, thatmay be crosslinked following deposition of the hole-transporting polymerto form the hole-transporting layer.

If present, an electron transporting layer located between thelight-emitting layers and cathode preferably has a LUMO level of around2.5-3.5 eV as measured by square wave cyclic voltammetry. A layer of asilicon monoxide or silicon dioxide or other thin dielectric layerhaving thickness in the range of 0.2-2 nm may be provided between thelight-emitting layer nearest the cathode and the cathode.

An electron transporting layer may contain a polymer comprising a chainof optionally substituted arylene repeat units, such as a chain offluorene repeat units.

HOMO and LUMO levels as described herein may be measured by cyclicvoltammetry (CV) as follows.

The working electrode potential is ramped linearly versus time. Whencyclic voltammetry reaches a set potential the working electrode'spotential ramp is inverted. This inversion can happen multiple timesduring a single experiment. The current at the working electrode isplotted versus the applied voltage to give the cyclic voltammogramtrace.

Apparatus to measure HOMO or LUMO energy levels by CV may comprise acell containing a tert-butyl ammonium perchlorate/or tertbutyl ammoniumhexafluorophosphate solution in acetonitrile, a glassy carbon workingelectrode where the sample is coated as a film, a platinum counterelectrode (donor or acceptor of electrons) and a reference glasselectrode no leak Ag/AgCl. Ferrocene is added in the cell at the end ofthe experiment for calculation purposes. (Measurement of the differenceof potential between Ag/AgCl/ferrocene and sample/ferrocene).

Method and Settings:

3 mm diameter glassy carbon working electrode

Ag/AgCl/no leak reference electrode

Pt wire auxiliary electrode

0.1 M tetrabutylammonium hexafluorophosphate in acetonitrile

LUMO=4.8−ferrocene (peak to peak maximum average)+onset

Sample: 1 drop of 5 mg/mL in toluene spun @3000 rpm LUMO (reduction)measurement:

A good reversible reduction event is typically observed for thick filmsmeasured at 200 mV/s and a switching potential of −2.5V. The reductionevents should be measured and compared over 10 cycles, usuallymeasurements are taken on the 3^(rd) cycle. The onset is taken at theintersection of lines of best fit at the steepest part of the reductionevent and the baseline.

Hole Injection Layers

A conductive hole injection layer, which may be formed from a conductiveorganic or inorganic material, may be provided between the anode and thelight-emitting layer or layers to assist hole injection from the anodeinto the layer or layers of semiconducting polymer. A hole transportinglayer may be used in combination with a hole injection layer.

Examples of doped organic hole injection materials include optionallysubstituted, doped poly(ethylene dioxythiophene) (PEDT), in particularPEDT doped with a charge-balancing polyacid such as polystyrenesulfonate (PSS) as disclosed in EP 0901176 and EP 0947123, polyacrylicacid or a fluorinated sulfonic acid, for example Nafion®; polyaniline asdisclosed in U.S. Pat. No. 5,723,873 and U.S. Pat. No. 5,798,170; andoptionally substituted polythiophene or poly(thienothiophene). Examplesof conductive inorganic materials include transition metal oxides suchas VOx, MoOx and RuOx as disclosed in Journal of Physics D: AppliedPhysics (1996), 29(11), 2750-2753.

Cathode

The cathode is selected from materials that have a work functionallowing injection of electrons into the light-emitting layer or layers.Other factors influence the selection of the cathode such as thepossibility of adverse interactions between the cathode and thelight-emitting materials. The cathode may consist of a single materialsuch as a layer of aluminium. Alternatively, it may comprise a pluralityof metals, for example a bilayer of a low work function material and ahigh work function material such as calcium and aluminium as disclosedin WO 98/10621. The cathode may contain a layer containing elementalbarium, for example as disclosed in WO 98/57381, Appl. Phys. Lett. 2002,81(4), 634 and WO 02/84759 or a layer containing elemental magnesium.The cathode may contain a thin (e.g. 1-5 nm thick) layer of metalcompound between the light-emitting layer(s) of the OLED and one or moreconductive layers of the cathode, such as one or more metal layers.Exemplary metal compounds include an oxide or fluoride of an alkali oralkali earth metal, to assist electron injection, for example lithiumfluoride as disclosed in WO 00/48258; barium fluoride as disclosed inAppl. Phys. Lett. 2001, 79(5), 2001; and barium oxide. In order toprovide efficient injection of electrons into the device, the cathodepreferably has a work function of less than 3.5 eV, more preferably lessthan 3.2 eV, most preferably less than 3 eV. Work functions of metalscan be found in, for example, Michaelson, J. Appl. Phys. 48(11), 4729,1977.

The cathode may be opaque or transparent. Transparent cathodes areparticularly advantageous for active matrix devices because emissionthrough a transparent anode in such devices is at least partiallyblocked by drive circuitry located underneath the emissive pixels. Atransparent cathode comprises a layer of an electron injecting materialthat is sufficiently thin to be transparent. Typically, the lateralconductivity of this layer will be low as a result of its thinness. Inthis case, the layer of electron injecting material is used incombination with a thicker layer of transparent conducting material suchas indium tin oxide.

It will be appreciated that a transparent cathode device need not have atransparent anode (unless, of course, a fully transparent device isdesired), and so the transparent anode used for bottom-emitting devicesmay be replaced or supplemented with a layer of reflective material suchas a layer of aluminium. Examples of transparent cathode devices aredisclosed in, for example, GB 2348316.

Encapsulation

Organic optoelectronic devices tend to be sensitive to moisture andoxygen. Accordingly, the substrate 101 preferably has good barrierproperties for prevention of ingress of moisture and oxygen into thedevice. The substrate is commonly glass, however alternative substratesmay be used, in particular where flexibility of the device is desirable.For example, the substrate may comprise a plastic as in U.S. Pat. No.6,268,695 which discloses a substrate of alternating plastic and barrierlayers or a laminate of thin glass and plastic as disclosed in EP0949850.

The device may be encapsulated with an encapsulant (not shown) toprevent ingress of moisture and oxygen. Suitable encapsulants include asheet of glass, films having suitable barrier properties such as silicondioxide, silicon monoxide, silicon nitride or alternating stacks ofpolymer and dielectric as disclosed in, for example, WO 01/81649 or anairtight container as disclosed in, for example, WO 01/19142. In thecase of a transparent cathode device, a transparent encapsulating layersuch as silicon monoxide or silicon dioxide may be deposited to micronlevels of thickness, although in one preferred embodiment the thicknessof such a layer is in the range of 20-300 nm. A getter material forabsorption of any atmospheric moisture and/or oxygen that may permeatethrough the substrate or encapsulant may be disposed between thesubstrate and the encapsulant.

Solution Processing

Suitable solvents for forming solution processable formulations of thelight-emitting metal complex of formula (I) and compositions thereof maybe selected from common organic solvents, such as mono- orpoly-alkylbenzenes such as toluene and xylene and mono- orpoly-alkoxybenzenes, and mixtures thereof.

Exemplary solution deposition techniques for forming a light-emittinglayer containing a compound of formula (I) include printing and coatingtechniques such spin-coating, dip-coating, roll-to-roll coating orroll-to-roll printing, doctor blade coating, slot die coating, gravureprinting, screen printing and inkjet printing.

Coating methods, such as those described above, are particularlysuitable for devices wherein patterning of the light-emitting layer orlayers is unnecessary—for example for lighting applications or simplemonochrome segmented displays.

Printing is particularly suitable for forming a patterned light-emittinglayer. A device may be inkjet printed by providing a patterned layerover the first electrode and defining wells for printing. The patternedlayer is preferably a layer of photoresist that is patterned to definewells as described in, for example, EP 0880303.

As an alternative to wells, the ink may be printed into channels definedwithin a patterned layer. In particular, the photoresist may bepatterned to form channels which, unlike wells, extend over a pluralityof pixels and which may be closed or open at the channel ends.

The same coating and printing methods may be used to form other layersof an OLED including (where present) a hole injection layer, a chargetransporting layer and a charge blocking layer.

Applications

An organic light-emitting diode containing a compound of formula (I),preferably an infra-red emitting compound of formula (I) may be used,without limitation, in night vision goggles, sensors and CMOS chips

EXAMPLES Compound Example 1

Compound Example 1 was prepared according to Scheme 1

2-Bromo-9-(3,5-dihexylphenyl)-9-methyl-9H-fluorene

An oven dried 3 L four neck flask fitted with nitrogen inlet, overheadstirrer and dropping funnel was charged with2,7-dibromo-9-(3,5-dihexylphenyl)-9-methyl-9H-fluorene (71.0 g, 121.90mmol). Air was replaced with nitrogen for 30 min. Anhydrous THF (710 ml)was added and the flask was cooled down to −78° C. using dry ice/acetonebath. A solution of n-BuLi (2.5M, 40.0 ml, 100 mmol, 0.82 equivt.) wasadded dropwise over a period of 30 min and stirred for 1 hr. GC-MSanalysis of crude sample showed that it contained ˜30% startingdibromide. A further of 0.41 equivt of nBuLi (2.5M, 20.0 ml, 50 mmol)was added and stirred continued for 1.5 hr at −78° C. GC-MS analysisshowed no starting material left. The reaction mixture was allowed towarm to −45° C. and quenched with careful dropwise addition of 100 ml ofwater then allowed to increase temperature to RT overnight. The reactionwas stopped and transferred to a separatory funnel. Heptane (500 ml) andwater (200 ml) were added and allowed to separate. The organic layer wassuccessively washed with 10% NaCl (aq.) solution (100 ml×3) and withwater (200 ml×3) then dried over MgSO₄ and filtered. The solvent wasevaporated to about 150 ml then passed through a small pad of silica andeluted with heptane. The crude material was purified by columnchromatography using heptane as eluent (30.8 g, colourless oil, 49.8%yield, 98.8% HPLC).

¹H-NMR (600 MHz, CDCl₃, TMS): δ=7.74 (m, 1H), 7.61 (m, 1H), 7.45 (m,1H), 7.34 (m, 2H), 7.21 (m, 2H), 6.8 (m, 3H), 2.46 (t, 4H), 1.82 (s,3H), 1.47 (m, 4H), 1.26 (m, 12H), 0.86 (t, 6H).

2-(9-(3,5-Dihexylphenyl)-9-methyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane

In a 1 L three neck flask fitted with nitrogen inlet and condenser wereplaced 2-bromo-9-(3,5-dihexylphenyl)-9-methyl-9H-fluorene (30.7 g, 60.97mmol) and bis(pinacolato)diboron (17.03 g, 67.06 mmol, 1.10 equivt).Anhydrous dioxane (300 ml) was added and nitrogen was bubbled throughthe solution for 30 min. A suspension of dppf (1.01 g, 1.83 mmol) andPdCl₂(dppf).CH₂Cl₂ (1.49 g, 1.83 mmol) was added to the reactionmixture. Nitrogen bubbling was continued for another 30 min. Potassiumacetate (17.95 g, 182.9 mmol, 3.0 equivt) was added as solid and thereaction mixture was heated to 110° C. for 16 hr. The reaction wasstopped and allowed to cool to room temperature. It was then dilutedwith 200 ml EtOAc and transferred to a separatory funnel and allowed toseparate. The organic layer was then washed with water (500 ml×3) andbrine (200 ml×3) and dried over MgSO₄. Evaporation of solvent andpurification by silica column using 40% CH₂Cl₂/heptane gives the ester,(20.3 g, 97.61% HPLC, 61.5% yield) a viscous liquid which solidified onstanding for few days.

¹H-NMR (600 MHz, CDCl₃, TMS): δ=7.82 (m, 1H), 7.70 (m, 1H), 7.46 (m,1H), 7.35 (m, 2H), 7.20 (m, 2H), 6.82 (m, 3H), 2.46 (t, 4H), 1.88 (s,3H), 1.48 (m, 4H), 1.42 (s, 12H), 1.22 (m, 12H), 0.85 (t, 6H).

1,4-Dibromoisoquinoline

In a 250 ml three neck flask fitted with overhead stirrer and condenserwhich is also connected to a scrubber solution, 1-hydroxyisoquinoline(10 .g, 68.89 mmol) and PBr₅ (53.38 g, 124 mmol) were taken. Thereaction mixture was gradually heated to 140° C. At about 125° C.-130°C. the solid melts and a deep read solution obtained which on furtherheating converts to yellowish solid at −135° C. The reaction mixture washeated at this temperature for 10 min then allowed to cool to roomtemperature. The pale yellow solid was crushed and added in portionsinto ice with stirring to obtain a pale yellow powder which was filteredand washed with water (150 ml) and dried in an oven at 50° C. undervacuum. The crude solid was purified by recrystallisation fromEtOAc/heptane (14.1 g, 99.93% HPLC, 71.3% yield). ¹H-NMR (600 MHz,CDCl₃, TMS): δ=8.47 (s, 1H), 8.32 (d, 1H), 8.19 (m, 1H), 7.72 (m, 1H).

4-Bromo-1-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)isoquinoline

In a 1 L three neck flask fitted with nitrogen bubbler, overhead stirrerand condenser were taken2-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane(20.0 g, 36.32 mmol), 1,4-dibromoisoquinoline (10.42 g, 36.32 mmol),toluene (200 ml), t-BuOH (100 ml) and THF (130 ml). To this mixture 40%aq. solution of n-Bu4NOH (100 ml, 145 mmol) was added followed by water(50 ml). Nitrogen was bubbled through the reaction mixture for 1 hr. Thecatalyst, Pd(Ph₃P)₄ (1.26 g, 1.09 mmol) was to the reaction mixture andheated to 50° C. for 16 hr. The reaction was stopped and transferred toa separatory funnel and diluted with 200 ml of EtOAc and allowed toseparate. The aqueous layer was extracted with EtOAc and the combinedorganic layer was washed with water (200 ml×3) and brine (200 ml×2). Itwas then dried over MgSO₄, evapourated to dryness and purified by silicacolumn using 50% CH₂Cl₂/heptane as eluent (18.2, 99.13% HPLC, 79.4%yield, viscous liq.). ¹H-NMR (600 MHz, CDCl₃, TMS): δ=8.77 (s, 1H), 8.27(d, 1H), 8.02 (d, 1H), 7.92 (d, 1H), 7.85 (d, 1H), 7.77 (m, 1H), 7.68(d, 1H), 7.53 (m, 2H), 7.39 (m, 1H), 7.30 (d, 2H), 6.81 (m, 3H), 2.46(t, 4H), 1.92 (s, 3H), 1.48 (m, 4H), 1.21 (m, 12H), 0.81 (t, 6H).

1-(9-(3,5-Dihexylphenyl)-9-methyl-9H-fluoren-2-yl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinoline

In a 1 L three neck flask fitted with nitrogen inlet and condenser4-bromo-1-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)isoquinoline(21.96 g, 34.81 mmol), bis(pinacolato)diboron (9.72 g, 38.29 mmol, 1.10equivt) and potassium acetate (10.25 g, 104.43 mmol, 3.0 equivt) weretaken. Anhydrous dioxane (220 ml) was added and nitrogen was bubbledthrough the solution for 45 min. A suspension of PdCl₂(dppf).CH2Cl2(0.850 g, 1.04 mmol, 0.03 equivt) in dioxane was added into the reactionflask and nitrogen bubbling was continued for another 15 min. Thereaction mixture was heated to 110° C., the progress of reaction wasmonitored by HPLC analysis. After 16 hrs it still contained startingmaterial, bis(pinacolato)diboron (0.886 g, 3.48 mmol, 0.1 equvt) andfresh catalyst (0.01 eqvt) were added and heated for additional 24 hr.HPLC analysis showed no starting material left then the reaction wasstopped and allowed to cool to room temperature. It was then dilutedwith 200 ml EtOAc and transferred to a separatory funnel. It was thenwashed with water (400 ml×3) and brine (200 ml×3) and dried over MgSO₄.Evaporation of solvent gave a dark brown tar which was redissolved inEtOAc (200 ml) and treated with charcoal (40 g) twice and filtered.Evaporation of the solvent gives light brownish oil (20.92 g, 97.11%HPLC, 88.5% yield). ¹H-NMR (600 MHz, CDCl₃, TMS): δ=9.02 (s, 1H), 8.74(d, 1H), 8.02 (d, 1H), 7.92 (d, 1H), 7.84 (d, 1H), 7.69 (m, 2H), 7.57(s, 1H), 7.40 (m, 2H), 7.29 (m, 2H), 6.8 (m, 3H), 2.46 (t, 4H), 1.92 (s,3H), 1.49 (m, 4H), 1.43 (s, 12H), 1.20 (m, 12H), 0.83 (t, 6H).

4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)-1-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)isoquinoline

In a 1 L three neck flask fitted with nitrogen bubbler, overhead stirrerand condenser1-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)-4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinoline(20.92 g, 30.87 mmol),2,4-bis(4-(tert-butyl)phenyl)-6-chloro-1,3,5-triazine (10.55 g, 27.78mmol, 0.9 equivt), toluene (200 ml) and 20% aq. solution of n-Et₄NOH (90ml, 123 mmol) was added. Nitrogen was bubbled through the reactionmixture for 1 hr. To the reaction mixture Pd(Ph₃P)₄ (1.07 g, 0.93 mmol)was added and nitrogen bubbling was continued for another 15 min thenheated to 70° C. for 16 hr. Sampling showed no2,4-bis(4-(tert-butyl)phenyl)-6-chloro-1,3,5-triazine left then thereaction was stopped, cooled down to room temperature and transferred toa separatory funnel. The aqueous layer was extracted with EtOAc and thecombined organic layer was washed with water (200 ml×3) and brine (200ml×2). It was then dried over MgSO₄, evaporated to dryness and purifiedby silica column using 30% CH₂Cl₂/heptane as eluent giving paleyellowish liquid. The product was further purified and solidified bystirring in methanol and repeatedly precipitated from CH₂Cl₂/MeOH (13.5g, pale yellow powder, 99.5% HPLC, 51.5% yield). ¹H-NMR (600 MHz, CDCl₃,TMS): δ=9.62 (s, 1H), 9.30 (d, 1H), 8.7 (d, 4H), 8.17 (d, 1H), 7.97 (d,1H), 7.88 (d, 1H), 7.81 (m, 2H), 7.68 (s, 1H), 7.62 (d, 4H), 7.54 (m,1H), 7.41 (m, 1H), 7.32 (m, 2H), 6.8 (m, 3H), 2.47 (t, 4H), 1.96 (s,3H), 1.51 (m, 4H), 1.41 (s, 18H), 1.25 (m, 12H), 0.83 (t, 6H).

Ir{4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)-1-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)isoquinoline}2acac

In a 250 ml three neck flask fitted with overhead stirrer, nitrogeninlet and condenser4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)-1-(9-(3,5-dihexylphenyl)-9-methyl-9H-fluoren-2-yl)isoquinoline(6.5 g, 7.26 mmol), IrCl3.3H2O (1.02 g, 2.90 mmol), 2-ethoxy ethanol (70ml) and water (23 ml) were taken. Nitrogen was bubbled through thereaction mixture for 1 hr then heated to 120° C. for 16 hr beforecooldown to room temperature. The solid was filtered, washed with waterand dried in oven at 50° C. under vacuum. The material was used for thenext step without further purification.

A 250 ml three neck flask fitted with overhead stirrer, nitrogen inletand condenser was charged with the material from previous step (6.5 g,2.96 mmol), acetyl acetone (8.890 g, 88.8 mmol, 30 equivt) and 2-ethoxyethanol (100 ml). Nitrogen was bubbled through the reaction mixture for1 hr then solid Na₂CO₃ (2.83 g, 26.64 mmol, 9 equivt) was added into theflask. The reaction mixture was heated to 120° C. for 16 hr beforecooldown to room temperature. Water (60 ml) was added to precipitate thesolid which was filtered, washed with water and dried in oven at 50° C.under vacuum. The material was purified by silica gel columnchromatography using 30% CH₂Cl₂/heptane as eluent. The main diastereomerwas collected and further purified by precipitation from CH₂Cl₂/MeOH(1.56 g, >99.5% HPLC).

¹H-NMR (600 MHz, THF-d₈): δ=9.75 (s, 1H), 9.72 (s, 1H), 9.67 (s, 1H),9.66 (s, 1H), 8.97 (m, 2H), 8.73 (m, 8H), 8.23 (s, 1H), 8.19 (s, 1H),7.94 (m, 2H), 7.82 (m, 2H), 7.61 (m, 8H), 7.06 (m, 14H), 6.75 (s, 1H),6.73 (s, 1H), 5.43 (s, 1H), 2.39 (m, 8H), 1.82 (m, 12H), 1.47 (m, 8H),1.37 (m, 36H), 1.2 (m, 24H), 0.83 (t, 6H), 0.79 (t, 6H).

Compound Example 2

Compound Example 2 was prepared according to Scheme 2:

1,3-dihexyl-5-iodobenzene

An oven dried 2 L four neck flask fitted with nitrogen inlet, overheadstirrer and dropping funnel was charged with 1-bromo-3,5-dihexylbenzene(50.0 g, 153.69 mmol). Air was replaced with nitrogen for 30 min.Anhydrous THF (400 ml) was added and the flask was cooled down to −78°C. using dry ice/acetone bath. A solution of n-BuLi (2.5M, 80.0 ml, 200mmol, 1.3 equivt.) was added dropwise over a period of 30 min andstirred for 1 hr at −78° C. A THF solution (150 ml) of iodine (50.71 g,200 mmol) was added dropwise into the reaction mixture at −78° C. thenallowed to warm to room temperature and stirred for 16 hr. The reactionwas quenched with aqueous sodium thiosulphate solution (200 ml) thentransferred to a separatory funnel. The aqueous layer was extracted withheptane and the combined organic layers were washed with water (200ml×2) and brine (200 ml×2). It was then dried over MgSO₄ andconcentrated to about 200 ml then passed through a pad of silica andeluted with heptane. The solvent was evaporated and dried in oven at 50°C. under vacuum (49.5 g, 64% yield). GC-MS analysis shows it containstraces of starting bromide. The material was used for the next stepwithout further purification.

¹H-NMR (600 MHz, THF-d₈): δ=7.34 (s, 2H), 6.92 (s, 1H), 2.50 (t, 4H),1.56 (m, 4H), 1.2 (m, 12H), 0.88 (t, 6H).

2-bromo-9-(3,5-dihexylphenyl)-9H-carbazole

A 2 L flask fitted with overhead stirrer and condenser was charged with1,3-dihexyl-5-iodobenzene (9.0 g, 36.57 mmol) and 2-bromocarbazole(27.23 g, 73.14 mmol, 2 equivt). O-xylene (370 ml) was added andstirred. Nitrogen was bubbled through the suspension for 1 hr then KOHpellets (5.13 g, 91.42 mmol, 2.5 equivt) was added and stirred for 10min. CuCl (1.08 g, 10.9 mmol, 0.3 equivt) was added followed by1,10-phenanthroline (3.95 g, 21.91 mmol, 0.6 equivt), a brownish cloudysolution obtained. The reaction mixture heated to 100° C. for 1 hr thenthe rest of CuCl (0.73 g, 7.37 mmol, 0.2 equivt) and 1,10-phenanthroline(2.64 g, 14.34 mmol, 0.4 equivt) were added. The temperature of thereaction mixture was increased to 140° C. and heated for 20 hr. TLCshowed no bromocarbazole remained. The reaction was allowed to cool toroom temperature which resulted in the formation of a large amount ofblack precipitate. Water (300 ml) was added and stirred for 10 min thentransferred to a separatory funnel and allowed to separate. The aqueouslayer was extracted with EtOAc and the combined organic layer was washedwith water (200 ml×2) and brine (200 ml×2), dried over MgSO4, evaporatedto dryness, a brownish liquid which was purified by silica column usingheptane as eluent (17.05 g, colorless oil, 99.75% HPLC, 95% yield).

¹H-NMR (600 MHz, CDCl₃, TMS): δ=8.10 (d, 1H), 7.98 (d, 1H), 7.52 (d,1H), 7.42 (m, 1H), 7.37 (m, 2H), 7.29 (m, 1H), 7.13 (m, 3H), 2.69 (t,4H), 1.68 (m, 4H), 1.36 (m, 12H), 0.90 (t, 6H).

9-(3,5-Dihexylphenyl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole

In a 1 L three neck flask fitted with nitrogen inlet and condenser2-bromo-9-(3,5-dihexylphenyl)-9H-carbazole (17.0 g, 34.66 mmol) andbis(pinacolato)diboron (9.68 g, 38.12 mmol, 1.10 equivt) were taken.Anhydrous dioxane (300 ml) was added and nitrogen was bubbled throughthe solution for 30 min. A suspension of dppf (0.58 g, 1.04 mmol) andPdCl₂(dppf).CH₂Cl₂ (0.85 g, 1.04 mmol) was added to the reactionmixture. Nitrogen bubbling was continued for another 30 min. Potassiumacetate (10.20 g, 103.97 mmol, 3.0 equivt) was added as solid and thereaction mixture was heated to 110° C. for 16 hr, a pale brownishsolution obtained. The reaction was stopped and cooldown to roomtemperature. It was then diluted with 200 ml EtOAc and transferred to aseparatory funnel and allowed to separate. The organic layer was washedwith water (200 ml×3) and brine (150 ml) and dried over MgSO₄. Thesolvent was evaporated to dryness giving a pale brown liquid which wasdiluted with heptane and passed through a pad of celite/florosil (20g/20 g) and eluted with heptane. Evaporation of solvent gives lightyellowish liquid (17.08 g, 99.4% HPLC, 92% yield).

¹H-NMR (600 MHz, CDCl₃, TMS): δ=8.15 (m, 2H), 7.8 (s, 1H), 7.73 (m, 1H),7.40 (m, 2H), 7.2 (m, 1H), 7.16 (s, 2H), 7.10 (s, 1H), 2.69 (t, 4H),1.69 (m, 4H), 1.37 (m, 24H), 0.89 (t, 6H).

2-(4-bromoisoquinolin-1-yl)-9-(3,5-dihexylphenyl)-9H-carbazole

In a 1 L three neck flask fitted with nitrogen bubbler, overhead stirrerand condenser were taken9-(3,5-Dihexylphenyl)-2-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole(17.08 g, 30.94 mmol), 1,4-dibromoisoquinoline (9.26 g, 32.27 mmol),toluene (170 ml), t-BuOH (85 ml) and THF (111 ml). To this mixture 40%aq. solution of n-Bu₄NOH (80 ml, 123 mmol) was added followed by water(42 ml). Nitrogen was bubbled through the reaction mixture for 1 hr. Thecatalyst, Pd(Ph₃P)₄ (1.07 g, 0.93 mmol) was to the reaction mixture andheated to 50° C. for 16 hr. The reaction was stopped and transferred toa separatory funnel and diluted with 200 ml of EtOAc and allowed toseparate. The aqueous layer was extracted with EtOAc and the combinedorganic layer was washed with water (200 ml×3) and brine (200 ml×2). Itwas then dried over MgSO₄, evaporated to dryness and purified by silicacolumn using 40% CH₂Cl₂/heptane as eluent (16.2, 99.65% HPLC, 83% yield,pale brown oil).

¹H-NMR (600 MHz, CDCl₃, TMS): δ=8.78 (s, 1H), 8.23 (m, 4H), 7.81 (m,1H), 7.71 (s, 1H), 7.56 (m, 2H), 7.4 (m, 2H), 7.32 (m, 1H), 7.21 (s,2H), 7.05 (s, 1H), 2.64 (t, 4H), 1.62 (m, 4H), 1.33 (m, 4H), 1.24 (m,8H), 0.84 (t, 6H).

9-(3,5-dihexylphenyl)-2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinolin-1-yl)-9H-carbazole

In a 1 L three neck flask fitted with nitrogen inlet and condenser2-(4-bromoisoquinolin-1-yl)-9-(3,5-dihexylphenyl)-9H-carbazole (15.86 g,25.68 mmol), bis(pinacolato)diboron (7.17, 28.24 mmol, 1.10 equivt) andpotassium acetate (7.56 g, 77.03 mmol, 3.0 equivt) were taken. Anhydrousdioxane (160 ml) was added and nitrogen was bubble through the solutionfor 45 min. A suspension of PdCl₂(dppf).CH₂Cl₂ (0.630 g, 0.77 mmol, 0.03equivt) in dioxane was added into the reaction flask and nitrogenbubbling was continued for another 15 min. The reaction mixture washeated to 110° C., the progress of reaction was monitored by HPLCanalysis and once no starting material left then it was stopped andcooldown to room temperature. It was then diluted with 150 ml EtOAc andtransferred to a separatory funnel. It was then washed with water (300ml×3) and brine (150 ml×2) and dried over MgSO₄. Evaporation of solventgiving brown tar which was redissolved in toluene (100 ml) and passedthrough a pad of celite/florosil (30 g/50 g) and eluted with 1 L oftoluene. Evaporation of the solvent gives light brownish oil (12 g, 97%HPLC, 67% yield). The material was used for the next step withoutfurther purification.

¹H-NMR (600 MHz, CDCl₃, TMS): δ=9.03 (s, 1H), 8.70 (d, 1H), 8.23 (m,3H), 7.17 (m, 2H), 7.49 (m, 4H), 7.32 (m, 1H), 7.22 (s, 2H), 7.03 (s,1H), 2.63 (t, 4H), 1.61 (m, 4H), 1.44 (s, 12H), 1.32 (m, 4H), 1.24 (m,8H), 0.84 (t, 6H).

2-(4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)isoquinolin-1-yl)-9-(3,5-dihexylphenyl)-9H-carbazole

In a 1 L three neck flask fitted with nitrogen bubbler, overhead stirrerand condenser9-(3,5-dihexylphenyl)-2-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)isoquinolin-1-yl)-9H-carbazole(11.00 g, 14.54 mmol),2,4-bis(4-(tert-butyl)phenyl)-6-chloro-1,3,5-triazine (5.52 g, 14.54mmol, 1.0 equivt), toluene (110 ml) and 20% aq. solution of n-4NOH (42ml, 58.16 mmol) was added. Nitrogen was bubbled through the reactionmixture for 1 hr. To the reaction mixture Pd(Ph₃P)₄ (0.5 g, 0.44 mmol)was added and nitrogen bubbling was continued for another 15 min thenheated to 70° C. for 16 hr. Sampling shows no starting materials leftthen the reaction was stopped, cool down to RT and transferred to aseparatory funnel. The aqueous layer was extracted with EtOAc and thecombined organic layer was washed with water (100 ml×3) and brine (100ml×2). It was then dried over MgSO₄, evaporated to dryness and purifiedby silica column using 30% CH₂Cl₂/heptane as eluent giving paleyellowish liquid. The product was further purified and solidified bystirring in methanol and repeatedly precipitated from CH₂Cl₂/MeOH (11.8g, pale yellowish powder, 99.49% HPLC, 81.5% yield).

¹H-NMR (600 MHz, CDCl₃, TMS): δ=9.03 (s, 1H), 8.76 (d, 1H), 8.22 (m,4H), 7.70 (m, 3H), 7.58 (m, 1H), 7.45 (m, 4H), 7.31 (m, 1H), 7.25 (m,6H), 7.16 (m, 1H), 7.03 (s, 1H), 2.63 (t, 4H), 1.62 (m, 4H), 1.44 (m,12H), 1.27 (m, 18H), 0.84 (t, 6H).

Ir{2-(4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)isoquinolin-1-yl)-9-(3,5-dihexylphenyl)-9H-carbazole}2acac

In a 100 ml three neck flask fitted with overhead stirrer, nitrogeninlet and condenser2-(4-(4,6-bis(4-(tert-butyl)phenyl)-1,3,5-triazin-2-yl)isoquinolin-1-yl)-9-(3,5-dihexylphenyl)-9H-carbazole(1.3 g, 1.47 mmol), IrCl₃.3H2O (0.24 g, 0.67 mmol), 2-ethoxy ethanol (25ml) and water (8 ml) were taken. Nitrogen was bubbled through thereaction mixture for 1 hr then heated to 120° C. for 16 hr beforecooldown to room temperature. The solid was filtered, washed with waterand dried in oven at 50° C. under vacuum. The material was used for thenext step without further purification.

A 100 ml three neck flask fitted with overhead stirrer, nitrogen inletand condenser was charged with the material from previous step (1.42 g,0.64 mmol), acetyl acetone (1.92 g, 19.21 mmol, 30 equivt) and 2-ethoxyethanol (40 ml). Nitrogen was bubbled through the reaction mixture for 1hr then solid Na₂CO₃ (0.61 g, 5.76 mmol, 9 equivt) was added into theflask. The reaction mixture was heated to 120° C. for 16 hr beforecooldown to room temperature. Water (50 ml) was added to precipitate thesolid which was filtered, washed with water and MeOH and dried in ovenat 50° C. under vacuum. The material was purified by silica gel columnchromatography using 40% CH₂Cl₂/heptane as eluent. The product furtherpurified by precipitation from CH₂Cl₂/MeOH (0.34 g, 99.5% HPLC, 26%yield).

¹H-NMR (600 MHz, CDCl3, TMS): δ=9.75 (s, 2H), 9.55 (d, 2H), 9.03 (d,2H), 8.72 (d, 8H), 8.42 (s, 2H), 7.86 (m, 2H), 7.72 (m, 2H), 7.56 (m,10H), 7.31 (s, 2H), 7.19 (m, 8H), 7.04 (s, 2H), 6.89 (m, 2H), 5.40 (s,1H), 2.60 (t, 8H), 1.87 (s, 6H), 1.70 (m, 8H), 1.35 (m, 66H), 0.90 (t,6H).

Device Examples

Devices having the following structure were prepared:

ITO/HIL (65 nm)/HTL (22 nm)/LEL (80-140 nm)/Cathode

in which ITO is an indium tin oxide anode; HIL is a hole-injectionlayer; HTL is a hole-transporting layer; and LEL is a light-emittinglayer.

To form the device, a substrate carrying ITO was cleaned using UV/Ozone.The hole injection layer was formed by spin-coating an aqueousformulation of a hole-injection material and heating the resultantlayer. The hole transporting layer was formed by spin-coatingHole-Transporting Polymer 1 and crosslinking the polymer by heating. Thelight-emitting layer was formed by spin-coating composition of CompoundExample 1 (7.5 wt %) and Host 1, 2 or 3 (92.5 wt %) from toluenesolution. The cathode was formed by evaporation of a first layer ofsodium fluoride to a thickness of about 4 nm, a second layer ofmagnesium to a thickness of about 1 nm and a third layer of silver to athickness of about 100 nm.

Hole Transporting Polymer 1 was formed by Suzuki polymerisation asdescribed in WO 00/53656 of fluorene repeat units of formula (VIII);amine repeat units of formula (VI-1); and crosslinkable repeat units offormula (VIII).

Host 1 is the polymer “F8BT” formed by Suzuki polymerisation asdescribed in WO 00/53656 and having formula:

Hosts 2 and 3 are polymers that were formed by Suzuki polymerisation asdescribed in WO 00/53656 of the monomers set out in Table 1.

TABLE 1 Repeat unit Host 2 (mol %) Host 3 (mol %)

36 36

14 15

32.5 12.5

 7.5  7.5

10 30

A comparative device was formed by the same process except that CompoundExample 1 was replaced with Comparative Compound 1:

Comparative Compound 1

Device performance is summarised in Table 2, in which voltages, externalquantum efficiencies and power density were measured at a currentdensity of 50 mA/cm².

TABLE 2 Voltage EQE Power density Device Host Emitter (V) (%) (mW/cm²)Comparative Host 1 Comparative 12.5 0.78 0.62 Device 1 Compound 1 DeviceHost 1 Compound 11.1 1.10 0.92 Example 1 Example 1 Device Host 2Compound 9.9 3.12 2.60 Example 2 Example 1 Device Host 3 Compound 11.078.02 6.67 Example 3 Example 1

In all cases, the exemplary devices require lower drive voltage and havehigher efficiency and power density than Comparative Device 1 at thereference current density.

Although the present invention has been described in terms of specificexemplary embodiments, it will be appreciated that variousmodifications, alterations and/or combinations of features disclosedherein will be apparent to those skilled in the art without departingfrom the scope of the invention as set forth in the following claims.

1. A compound of formula (I):

wherein: M is a transition metal; Ar¹ is a 5 or 6 membered heteroarylring or a polycyclic heteroaromatic group; Ar² is a polycyclic groupcomprising two or more rings selected from aromatic and heteroaromaticrings; Ar¹ and Ar² may be linked by a direct bond or divalent linkinggroup; L is a ligand; x is at least 1; y is 0 or a positive integer; ais 0 or a positive integer; b is 0 or a positive integer; R¹, R² and R³are each independently a substituent; and (i) Ar¹ is a polycyclicheteroaromatic group; or (ii) Ar¹ is a 5 or 6 membered heteroaryl ringand Ar² is a polycyclic group comprising at least 3 rings selected fromaromatic and heteroaromatic rings.
 2. A compound according to claim 1wherein M is Ir³⁺.
 3. A compound according to claim 1 wherein x is 2 or3.
 4. A compound according to claim 1 wherein y is 0 or
 1. 5. A compoundaccording to claim 1 wherein Ar¹ is a polycyclic heteroaromatic group.6. A compound according to claim 5 wherein Ar¹ is isoquinoline.
 7. Acompound according to claim 1 wherein Ar² is selected from the groupconsisting of:

wherein X in each occurrence is independently CR² ₂, SiR² ₂, NR², O orS, and * is a bond to Ar¹.
 8. A compound according to claim 1 wherein R¹and R² are independently in each occurrence selected from the groupconsisting of: C1-20 alkyl wherein one or more non-adjacent C atoms ofthe C1-20 alkyl may be replaced with —O—, —S—, C═O or —COO— and one ormore H atoms may be replaced with F; and a group of formula —(Ar3)pwherein Ar3 in each occurrence is a C6-20 aryl group or a 5-20 memberedheteroaryl group that may be unsubstituted or substituted with one ormore substituents; and p is at least
 1. 9. A compound according to claim1 wherein R³ in each occurrence is independently selected from the groupconsisting of: C₁₋₂₀ alkyl wherein one or more non-adjacent C atoms ofthe C₁₋₂₀ alkyl may be replaced with —O—, —S—, C═O or —COO— and one ormore H atoms may be replaced with F; and a group of formula —(Ar⁴)qwherein Ar⁴ in each occurrence is a C₆₋₂₀ aryl group or a 5-20 memberedheteroaryl group that may be unsubstituted or substituted with one ormore substituents; and q is at least
 1. 10. A compound according toclaim 9 wherein R³ in each occurrence is a C₆₋₂₀ aryl group that may beunsubstituted or substituted with one or more substituents.
 11. Acompound according to claim 1 wherein the compound has aphotoluminescent spectrum having a peak wavelength greater than 650 nm.12. A composition comprising a host material and a compound according toclaim
 1. 13. A composition according to claim 12 wherein the hostmaterial is a polymer comprising a repeat unit of formula (V)

wherein Ar⁵ and Ar⁶ are each independently aryl or heteroaryl that maybe unsubstituted or substituted with one or more substituents; u and vin each occurrence is independently at least 1; R⁶ is a substituent; andY is N or CR⁹, wherein R⁹ is H or a substituent, with the proviso thatat least one Y is N.
 14. A composition according to claim 13 wherein atleast one of Ar⁵ and Ar⁶ is a C₁₀₋₂₀ aryl group.
 15. A compositionaccording to claim 13 wherein R⁶ is a group of formula —(Ar⁷)w whereinAr⁷ independently in each occurrence is an aryl or heteroaryl group thatmay be unsubstituted or substituted with one or more substituents and wis at least
 1. 16. A composition according to claim 15 wherein the oreach group Ar⁷ is selected from phenyl and pyridyl, each of which may beunsubstituted or substituted with one or more substituents.
 17. Asolution comprising a compound or composition according to claim 1dissolved in one or more solvents.
 18. An organic light-emitting devicecomprising an anode, a cathode and a light-emitting layer between theanode and cathode wherein the light-emitting layer comprises a compoundor composition according to claim
 1. 19. A method of forming an organiclight-emitting device according to claim 18 comprising the step ofdepositing the light-emitting layer over one of the anode and cathode,and depositing the other of the anode and cathode over thelight-emitting layer.
 20. A method according to claim 19 wherein thelight-emitting layer is formed by depositing a solution comprising thecompound dissolved in one or more solvents and evaporating the one ormore solvents.